1. Field of the Invention
The present invention relates to a mechanism element for optical devices such as video cameras, telephoto lenses, copiers, laser printers, facsimile machines, or the like, and in particular, relates to a mechanism in which light absorption can be maintained over a wide range of wavelengths.
2. Description of the Related Art
In optical devices such as video cameras up until now, aluminum or alloys of aluminum or magnesium are desirably used as materials for a mechanism element of lensbarrels or the like which hold an optical system elements such as lens system elements from the viewpoint of solidness, workability, manufacturing accuracy, and weight minimization.
Generally, the surfaces of mechanism elements which hold optical system elements are black to reduce stray light due to reflection of incident light. Therefore, in the case in which a mechanism element is produced from the materials mentioned above, it is common for the surfaces of the mechanism element to be blackened after an anodizing treatment by using a black organic dye (hereinafter simply referred to as a “dye”). This blackening process is performed as follows: pores are formed on the surface of the mechanism element by an anodizing treatment, the dye is absorbed into the pores, and the dye is sealed in the pores by a sealing treatment. Alternatively, if a mechanism element is formed of a material which cannot be blackened by the blackening process described above, a black coating can be formed on the surface of the mechanism element. Furthermore, a mechanism element formed by a synthetic resin in which carbon black is mixed may also be provided.
In the a coating technique in which a black coating is used, large dimensional variations may occur due to uneven thickness of the coated film, and furthermore, in a case in which this is used in conditions in which the surface is pressed or rubbed. This is not desirable because the coated film may be partially peeled off forming contaminating matter. Furthermore, in the case in which the optical device is used in outer space, the coated film may be degraded by radiation or volatile components may be emitted. Mechanism elements formed from synthetic resins also have such drawbacks.
On the other hand, because the surface on which an anodizing treatment and a blackening treatment using a black dye are performed absorbs visible light well, exhibits solid characteristics, and dimensional variation due to the coated film and peeling of the coated film do not occur, it is desirable for mechanisms which hold optical system elements such as lens systems. In addition, in the case in which such mechanism elements are used in an optical device to be used in outer space, volatile component content is low, and degradation by radiation can be controlled because the dye is sealed in the pores.
However, in the blackening treatment using a black dye, the following problems have occurred.
(1) The surface of a mechanism element which is blackened using a black dye exhibits low reflectance of 5 to 10% in a wavelength range of 400 to 700 nm, which is in the visible region, and absorbs 90 to 95% of incident light. However, the reflectance gradually increases in the wavelength region above 700 nm. Specifically, the reflectance reaches 40% at 800 nm, 50% at 900 nm, 60% at 1000 nm, and about 80% at 1600 nm. Therefore, although incident light which is reflected by the mechanism element is reduced to 5 to 10% in an optical system for light having wavelengths of 400 to 700 nm, on the other hand, light having a wavelength of 1000 nm, for example, is reduced only to 60%. Actually, such light may be reflected many times in the mechanism element as stray light. For example, in the case of light having a wavelength of 1000 nm, if the light is reflected in the mechanism element two times, 36% of the light becomes stray light. As explained above, in the conventional technique in which the black dye is used, the quantity of stray light is increased by using the device in a wavelength region above 700 nm, and the efficiency of the optical device is deteriorated.(2) As described above, a blackening process is performed by absorption of black dye into pores of an anodized coating, but the dye can be filled into only about one-third of the depth of the pores because the pores are extremely narrow. On the other hand, if the anodized coating is formed thickly, part of the thickness of the material becomes uneven and the overall thickness also becomes uneven, and furthermore, if the pores are formed to be deep, this results in uneven filled amounts of the dye. Therefore, the anodized coating must be formed to be relatively thick in anticipation of the uneven filled amount of the dye. As a result, to yield a reflectance in the visible light region within a range of 5 to 10%, the thickness of the anodized coating must be more than 15 μm which is further thicker than the required filled depth of the dye. Therefore, the thickness of the anodizing coating is very uneven, and it is difficult to maintain dimensional accuracy of mechanism elements.